1. Field of the Invention
The present invention relates to a method for forming a pattern, and more particularly to a method for forming a pattern for preventing the generation of water marks on a semiconductor substrate during drying of the semiconductor substrate after forming an insulating layer of a semiconductor device.
2. Prior Art
Generally, an insulating layer stacked on a semiconductor substrate is patterned into a predetermined shape by using a photolithography process for forming a mask, and using a wet etching process or a dry etching process.
FIGS. 1A & 1B illustrate a method for forming a pattern on a semiconductor substrate using a conventional wet etching process. Referring to FIG. 1A, an insulating layer 12 is firstly formed on a semiconductor substrate 10 by depositing an insulating material such as silicon oxide to have a predetermined thickness and then a photoresist layer 14 is formed on insulating layer 12 by coating a photoresist through a spin-coating method. Next, an opening 16 for exposing a portion of insulating layer 12 to be etched, is formed by pre-baking, exposing by using a mask having a predetermined pattern and then developing photoresist layer 14 by a common photo process. Photoresist pattern 14 is subject to hard-baking for increasing an etching resistance and an adhesiveness of photoresist pattern 14, and for removing remaining solvent.
Now, referring to FIG. 1B, insulating layer 12 is wet etched by using resist pattern 14 including opening 16 as an etching mask and using buffered oxide etchant (BOE: a mixture of NH.sub.4 F:HF=6:1 in volume ratio) as an etching solution which includes hydrogen fluoride. Then, a portion of insulating layer 12 exposed by opening 16 is removed to form an insulating pattern 12A. Next, semiconductor substrate 10 is rinsed in deionized water, and then dried in a dryer to remove the deionized water. Then, the remaining resist pattern 14 is removed by stripping.
Through the above-described method, after insulating layer 12 is patterned by using resist pattern 14 as an etching mask, semiconductor substrate 10 including the remaining resist pattern 14 is immersed into the deionized water, and then the deionized water is removed. At this time, a portion of the deionized water remains partially on semiconductor substrate 10. FIG. 2 illustrates deionized water 18 remaining on the exposed portion of semiconductor substrate 10 between insulating pattern 12A and an adjacent insulating pattern after the deionized water is removed.
The deionized water can be removed by a subsequent drying process. However, water marks are formed on the semiconductor substrate by the remaining deionized water. The water mark formed before forming a gate oxide layer becomes a contaminant. The water mark acts as an oxygen supplying source when the gate oxide layer is formed by a thermal oxidation process, to thereby form a locally thick oxide layer. This results in the electrical failure of the semiconductor device.
It is reported that the reason for the formation of the water mark depends on the wettability of silicon. (see: Effect of Drying Methods and Wettability of Silicon on the Formation of Water Marks in Semiconductor Processing by Jin-Goo Park and Michael F. Pas, J. Electrochem. Soc., Vol. 142, No. 6, pp2028-2031). According to Park et al., a hydrophilic wafer does not form the water marks by any kind of drying method such as a spin drying method, a vapor drying method, etc., while a hydrophobic wafer forms a lot of the water marks by the spin drying method. Further, a wafer having uniform hydrophilic surface or hydrophobic surface does not form the water marks during subsequent vapor drying. However, a wafer having a surface including both the hydrophilic portion and hydrophobic portion forms the water marks after isopropyl alcohol (IPA) vapor drying process after the patterning process. That is, a wafer having the hydrophilic surface, from which water can be removed uniformly during drying, does not form the water marks, while a wafer having a large difference in wettability of silicon forms a lot of the water marks. Accordingly, the difference in the wettability of the wafer surface plays an important role in formation of the water marks.
The wet etching process using hydrogen fluoride when forming the gate oxide layer is widely used. The surface of the semiconductor substrate or insulating layer exposed to the wet etching process using hydrogen fluoride has high hydrophobicity.
The resist pattern formed by the photoresist is made of organic materials and so is hydrophobic. The hydrophobicity of the resist pattern having such hydrophobicity is different from that of the surface of the semiconductor substrate or the insulating layer transformed to be hydrophobic. The water marks are thought to be formed because of these differences.